This invention is related to apparatus and a process for supporting and maintaining a continuous web product in a pass-line position through an electrolyte solution in a continuous electrochemical treatment operation, and in particular, it is directed to the use of rigid, non-conductive, non-polar bumper devices having a slick surface that contacts and maintains the continuous web in the pass-line position. The apparatus and process improves electrochemical treatment rates, prevents arcing between the continuous web and electrodes positioned adjacent the web pass-line, and produces a continuous electrochemically treated web product having minimal surface defects.
It is recognized, for example in applicant's prior U.S. Pat. No. 5,476,578, incorporated herein in its entirety by reference, that plating efficiency can be increased by using resilient wiper blades that contact and remove bubbles of hydrogen (surface film) from the strip during an electroplating operation. Surface film buildup depletes available electrolyte at the cathodic work surface and reduces plating rates. The resilient wiper blades sweep away the surface film, (depleted electrolyte) thereby creating a hydraulic inflow of fresh electrolyte at the work surface or interface. In the preferred embodiment, the U.S. Pat. No. 5,476,578 teaches using a resilient wiper blade arrangement that allows "ready escape of the depleted electrolyte and replacement with fresh electrolyte."
In U.S. Pat. No. 5,938,899, also incorporated herein in its entirety by reference, applicant teaches that during electroplating the composite barrier layer comprises a combination of: 1) hydrogen bubbles, 2) a micro-ion depletion layer, and 3) a thermal barrier. This composite barrier prevents, or at least reduces, a rapid exchange of depleted electrolyte with fresh electrolyte at the substrate interface being plated. If the electroplating process fails to provide a continuous supply of fresh electrolyte at the plating interface, the plating rate speed will fall off. Therefore, it is necessary for an efficient plating operation to include means for removing the composite barrier layer and for delivering fresh electrolyte to the plating interface.
With the understanding that the above prior patents demonstrate an improvement in the art, continuous use in production along with careful research has revealed some inherent problems in earlier teaching. For example, it has been found that resilient wiper blades can effectively remove the composite barrier layer from a plating interface. However, because such wiper blades are resilient, their flexibility, creates problems for operators when the gauge or weight of the web material is increased, and in particular, when such resilient wiper blades are used in a horizontal line, the heavier web material causes unwanted flexing in the wiper blades. In such instances, the wiper blades can collapse under the increased load and arc against the plating electrodes positioned adjacent the continuous web pass-line. Such arcing can also occur in a vertical plating operation if extreme web flutter occurs along the pass-line, or if the shape of the web is extraordinarily uneven. In such circumstances, the wavy, vertically moving web, can impact against the resilient wiper blades, cause them to flex or collapse, and arc against the plating electrodes that are vertically positioned along the pass-line.
Production operations have revealed that, in certain instances, dendrites or whiskers can grow on nicked or cut wiper blades and the dendrites can damage and reduce the surface quality of the finished electrochemically treated product. For instance, a metal substrate in sheet or strip form has thin sharp edges that move at very high speeds, about 1,800 feet per minute, through a continuous treatment line. If any web flutter or wobble occurs, the thin sharp edges will cut and nick the wiper blades and bumper devices that are used to wipe and maintain the web in its pass-line position. Such nicks and cuts may attract ions that become nuclei for dendrite or whisker growth in certain combinations of polymer materials submerged in electrolyte baths. As the dendrites enlarge and solidify, their abrasive properties scratch and damage the web surface.
Metal sheet and strip substrates can also have slivers or burrs along the strip edge. Such imperfections also cut and nick wiper blades and bumper devices, even in the absence of any web flutter, creating nuclei for dendrite or "barnacle" growth. Additionally to provide a continuous web, operators weld or join the leading and tailing ends of coiled sheet to provide an uninterrupted web that moves continuously through an electrochemical treatment operation. Such weld joints can also cut and nick wiper blades and bumper devices creating nuclei for dendrite growth.
Research work directed to eliminating dendrite growth has led to the unexpected discovery that if a non-polar material is used to manufacture the bumper devices of the present invention, dendrite growth is eliminated, or at least reduced to a level where it is of little concern. Tests were conducted using various materials to manufacture bumper devices before it was discovered that a non-polar, ultra high molecular weight polymer material, with a slick outer surface having a dry relative coefficient of sliding function to rolled steel of about 0.30 or lower, overcomes all of the aforementioned problems. One such exemplary ultra high molecular weight polymer material suitable for making the bumper devices of the present invention is GAR-DUR.RTM., manufactured by Garland Manufacturing Company, Saco, Me. Referring to the GAR-DUR.RTM. UHMW Technical Data Sheet, incorporated herein by reference.
Earlier patents teach using rigid plastic materials to prevent substrates from arcing against plating electrodes. For example, U.S. Pat. No. 4,828,653 discloses using a plurality of parallel rods (4) of a suitable insulating material. However, U.S. Pat. No. 4,828,653 fails to recognize the dendrite problem and completely fails to teach or suggest a solution for reducing or eliminating the dendrites that will form on the rods (4) if the invention is used in production.
U.S. Pat. Nos. 3,619,383, 3,619,384, 3,619,386, and 3,734,838, to Eisner disclose using non-conducting, bumper like devices between a substrate and electrode in a plating line. However, Eisner actually teaches away from the present invention by encouraging operators to scratch the surface of the plated substrate. In each instance, Eisner teaches impregnating his non-conducting bumper like devices with an abrasive grit to facilitate scratching the plated surface as it moves across his bumper.
Additionally, prior teaching fails to provide a positive or pressurized inflow of fresh electrolyte at the plating interface. As heretofore mentioned, the resilient wiper blades sweep away depleted electrolyte creating a natural forced hydraulic inflow of fresh electrolyte at the work surface. However, it must be remembered that if the electroplating process fails to provide a continuous, sufficient supply of fresh electrolyte at the plating interface, the plating rate speed will fall off, Therefore, it is very desirous to provide an inflow of fresh electrolyte to the electrochemical treatment interface at a positive pressure, the pressurized inflow being at a volume that will prevent a slowdown in treatment rate speed.